It is a problem in the field of cellular communications to efficiently and continuously meet the communications requirements of the passengers in multiple aircraft as the aircraft fly their routes and approach/depart airports.
A typical Air-To-Ground cellular communications network (including the Ground-To-Air link) consists of a number of terrestrial (ground) base stations, each of which provides a radio frequency coverage area in a predetermined volume of space, radially arranged around the cell site transmitting antenna. This terrestrial base station uses an antenna pattern which is less sensitive to the reception of ground-originating or ground-reflected signals and which antenna pattern is transmissive only in a skyward direction. The terrestrial base stations are geographically distributed, generally following a typical cellular communications network layout. Terrestrial base stations can also be co-located near airports to enable network coverage when aircraft are on the ground; in this case, the antenna patterns are optimized for terrestrially located aircraft. The boundaries of the coverage area of each terrestrial base station are substantially contiguous with that of neighboring sites so that the composite coverage of all of the terrestrial base stations in the Air-To-Ground cellular communications network generally provides coverage over the targeted area. Terrestrial base stations may provide either a single omni-cell of coverage using transceiver(s) associated with a single transmit and receive antenna system or multiple sectors within the cell of coverage, each with associated transceivers and the associated transmit and receive antennas. The advantage of the latter arrangement, with multiple sectors per terrestrial base station, is to allow provision of increased call handling capacity in the coverage area of that terrestrial base station.
The use of the traditional bidirectional communication channels to serve an aircraft is a limitation on the total radio frequency spectrum available and, therefore, limits the total available call handling capacity in any single cell. Thus, the radio frequency communications link between the aircraft and the terrestrial base stations of the Air-To-Ground cellular communications network has limited capacity, represents a single point of failure, and represents a call handoff problem in terms of call handling capacity of the serving terrestrial cell sites.
In order to increase the capacity, availability, and reliability of a bandwidth constrained wireless Air-To-Ground network, other methods are used to parse the usable spatial and temporal multi-dimensional region where aircraft are operating, such as those taught by the above-noted U.S. patent application Ser. No. 11/590,146. These methods taught in this Multi-Link Aircraft Cellular System include using two substantially orthogonal polarizations to effectively double the capacity of a given spectral allocation. Further, if Walsh code domain separation is added, additional increases in the call handling capacity of the Air-To-Ground cellular communications network are realized.
The implementation of the Multi-Link Aircraft Cellular System makes use of multiple physically separated antennas mounted on the aircraft, as well as the use of additional optional signal isolation and optimization techniques, to improve the call handling capacity of the Air-To-Ground cellular communications network. On the ground, base station antenna pattern shaping in azimuth, in elevation, in altitude, or in multiple planes further segments the multi-dimensional spatial region into multiple sectors, thereby improving system capacity through spatial frequency re-use.
All of the aforementioned capacity enhancement techniques are additive in nature. For example, using substantially orthogonal polarizations together with 6-sector azimuth base station antenna patterns has a linear multiplier effect on overall capacity of that given base station and associated aircraft. When the collective network capacity is considered, the smoothing or balancing of load peaks across multiple nodes provides enhanced peak load management from an overall systems perspective.
Thus, the Air-To-Ground cellular communications network can increase its traffic (data and voice) handling capacity on a per aircraft basis by sharing its traffic load among more than one terrestrial cell or sector and by making use of multiple physically separated antennas mounted on the aircraft and base station antenna pattern sectoring, as well as the use of additional optional signal isolation and optimization techniques such as the use of orthogonal polarizations.
However, even with these improvements, the overall bandwidth available to serve the subscriber wireless devices on the aircraft can be inadequate, especially when the passengers are engaged in high-bandwidth data communication sessions. The transmission of multi-media content to serve the occupants of a commercial airliner, especially with the larger size aircraft, requires a significant bandwidth. Therefore, what is needed is an advance in the art which solves the Air-To-Ground cellular communications network call handling capacity problem and dramatically improves system availability, system reliability, and system capacity.